1. Field of the Invention
The present invention relates to golf balls. Specifically, the present invention relates to golf balls including a first layer, a second layer, and an adhesive layer positioned between the first layer and the second layer.
2. Description of the Related Art
Golf players place importance on spin performance of golf balls. When a backspin rate is high, the run is short. It is easy for golf players to cause a golf ball, to which backspin is easily provided, to stop at a target point. When a sidespin rate is high, the golf ball tends to curve. It is easy for golf players to intentionally cause a golf ball, to which sidespin is easily provided, to curve. A golf ball having excellent spin performance has excellent controllability. In particular, advanced golf players place importance on controllability upon a shot with a short iron.
For golf players, durability of golf balls is also important. A golf ball that does not break even by repeated hitting is desired. In addition, a golf ball in which a scuff and a wrinkle are unlikely to occur in a cover when being hit with a short iron is desired.
In light of controllability, golf balls having various structures have been proposed. JPH11-137725 (US 2001/0002372, US 2002/0086744) discloses a golf ball that includes an inner cover formed from an ionomer resin and an outer cover formed from a thermoplastic elastomer. JP2001-54588 (U.S. Pat. No. 6,702,695) discloses a golf ball that includes an inner cover having a Shore D hardness of 45 to 61 and an outer cover having a Shore D hardness of 35 to 55. JP2006-34745 (US 2006/0025241) discloses a golf ball that includes a mid layer formed from an ionomer resin and a cover formed from a thermoplastic polyurethane elastomer. JP2006-289059 (US 2006/0211517) discloses a golf ball that includes a mid layer including a styrene block-containing thermoplastic elastomer and a cover formed from an ionomer resin.
In a golf ball including a mid layer (namely, an inner cover) and a cover, insufficient adhesion between the mid layer and the cover leads to breakage of the golf ball. The insufficient adhesion also leads to a scuff and a wrinkle in the cover. The insufficient adhesion further leads to loss of energy transfer when the golf ball is hit with a golf club. The loss impairs the resilience performance of the golf ball.
In the golf balls disclosed in the above four publications, an adhesive layer is present between the mid layer and the cover. The golf ball disclosed in JPH11-137725 includes an adhesive layer formed from a copolymer of an olefin compound and glycidyl methacrylate. The golf ball disclosed in JP2001-54588 includes an adhesive layer formed from a polyurethane or a chlorinated polyolefin. The golf ball disclosed in JP2006-34745 includes an adhesive layer formed from a two-component curing type epoxy resin. The golf ball disclosed in JP2006-289059 includes an adhesive layer formed from a reaction product of a carboxyl group-containing polyurethane and a polycarbodiimide.
In the conventional golf balls, the adhesion between the mid layer and the cover is insufficient. In a golf ball in which a flexible cover is used for the purpose of providing controllability, this adhesion is particularly insufficient.
An object of the present invention is to provide a golf ball having excellent adhesion between a first layer and a second layer.